Aromatic hydrocarbons having alkyl substituents are widely used in a variety of fields. For example, they are used as starting materials for polymers, as intermediates for dyes, drugs and agricultural chemicals, or as starting materials for liquid crystal polymers. It is well known that such aromatic compounds having alkyl substituents can be produced by reacting aromatic compounds with alkylating agents such as olefins and alcohols in the presence of catalysts such as alumina, silica-alumina and aluminum chloride.
However, when alkyl group-substituted aromatic hydrocarbons are intended to be produced by reacting certain aromatic compounds such as biphenyl and naphthalene with alkylating agents such as olefins in the presence of well known catalysts such as silica-alumina and aluminum chloride, the conversion of the aromatic compounds may be low or it is usually difficult to introduce the specific number of alkyl substituents into specific positions of the aromatic compounds.
For example, when dialkylbiphenyls used in the production of biphenols useful as starting materials for condensation polymers are intended to be obtained by reacting biphenyl with alkylating agents such as olefins, it is necessary to produce dialkylbiphenyls, particularly p,p'-dialkylbiphenyl from biphenyl in a good yield. However, catalysts capable of producing dialkylbiphenyls, particularly p,p'-dialkylbiphenyl from biphenyl in a good yield are not yet known.
Japanese Patent Publn. No. 3298/1967 discloses a process for alkylating an aromatic compound which comprises the step of reacting aromatic compounds or an aromatic compound having non-polar substituents with alkylating agents such as olefins, alkyl halides and alcohols at a temperature of no more than 315.degree. C. in the presence of aluminosilicate catalysts such as Zeolite X, zeolite Y and mordenite. According to this reference, benzene and naphthalene are used as the aromatic compounds to be alkylated in examples, and said reference teaches that Zeolite X ion exchanged by rare earth metals exhibits particularly high activity among the aluminosilicate catalysts used in alkylating such aromatic compounds. However, we have found that in case that biphenyl is reacted with the alkylating agents such as olefins in the presence of the catalysts such as silica-alumina, the ion exchanged Zeolite X by rare earth metals, Zeolite Y and hydrogen-type Zeolite X disclosed in Japanese Patent Publn. No. 3298/1967, the conversion of biphenyl is low and further the selectivity of p,p'-dialkylbiphenyl is also low.
In view of the facts as described above, we have carried out studies in order to find out catalysts which produce an alkyl group-substituted aromatic compound by reacting an aromatic compound with an alkylating agent such as an olefin, and increase the conversion of the aromatic compound and which can introduce the specific number of alkyl substituents into specific positions of the aromatic compound. We have now found that the advantages described above can be obtained by a specific catalyst. The present invention has been completed on the basis of such a discovery.
An object of the present invention is to provide a process for producing an alkyl group-substituted aromatic hydrocarbon comprising reacting an aromatic compound with an alkylating agent such as an olefin in the presence of a specific catalyst which are intended to solve the problems associated with the prior art with the increased conversion of the aromatic compound and which can introduce the specific number of alkyl groups into the specific positions of the aromatic compound.